Expression of Toll-Like Receptors in Chronic Histiocytic Intervillositis of the Placenta.

Chronic histiocytic intervillositis of the placenta (CHI) shows monocytic/histiocytic infiltration of the intervillous space. Placental malaria has a CHI-like histopathology and induces an aberrant expression of Toll-like receptors (TLR) 3, 7-9. We hypothesized that, similar to placental malaria, CHI could be associated with increased TLR expression. TLR1-10 and other inflammation-associated factors were analyzed by real-time PCR and immunohistochemistry. A total of 31 formalin-fixed and paraffin-embedded placenta samples were evaluated: CHI (n = 9), and for control purposes, villitis of unknown etiology (VUE, n = 8) and placentas without inflammation (n = 14). CHI shows increased expression of monocytic TLR1, a receptor which is involved in bacterial lipopolysaccharide (LPS)-induced inflammation. This could indicate a TLR1-mediated immune mechanism in the placenta (e.g. triggered by transient, clinically inapparent maternal bacteraemia) which leads to massive monocytic/histiocytic accumulation in the intervillous space. The increased expression of TLR1 with no increased expression of TLR3 and TLR7-9 is different from that in malaria.